The present invention includes to die-bonding solder materials used in die bond for fixing silicon chips or the like onto a base.
As pressure sensors to detect the pressure or the differential pressure, semiconductor pressure transducers using a semiconductor pressure sensor are known (example: Japanese Utility Model Laid-Open No. 59-135654 or the like).
FIG. 9 shows one conventional example of semiconductor pressure transducers 900 equipped with such a semiconductor pressure sensor.
This semiconductor pressure transducer is constructed by installing a base 902 on a carrier 901 and further installing a semiconductor pressure sensor 903 on the base 902.
The carrier 901 is made of an about 0.5 to 3 mm thick metal plate or ceramic plate. A pressure inlet hole 904 is provided at the center, while a conductive pin 906 is inserted near the periphery and hermetically sealed with a seal material 905 such as glass.
The base 902 is formed of an insulating material closely resembling the semiconductor pressure sensor 903 in linear expansion coefficient into a 1 to 5 mm tall cylindrical body. Besides, this base 902 has an insert hole 908 communicating with the above pressure inlet hole 904.
And, to enhance the solderability in joining the base 902 to the carrier 901 by soldering, the carrier 901 and the base 902 are jointed by using a solder material 907 in addition of a gilt simple substance or a nickel-plated simple substance or a product obtained after gilded on its nickel plated surface.
In joining the base 902 to the carrier 901, for example, with ceramic employed for the base 902, the solder material 907 (brazing material) placed between the junction surfaces 901a and 902a of the carrier 901 and the base 902 is heated with a joining jig to melt a solder material 907 for joining after the metallizing according to a conventional well-known method comprising baking Mo, Mn or the like to their joining surfaces 902a and overlapping a Ni or Au plated layer thereon. As a solder material 907, a Snxe2x80x94Ag series eutectic solder comprising Tin (Sn) and Gold (Au) is used and the thickness of the junction part is set generally to the order of 10 to 50 xcexcm.
Besides, the semiconductor pressure sensor 903 is made of n-type monocrystal silicon (Si) or the like and has a semiconductor substrate 909 electrostatically joined to the top surface of the base 902. On this semiconductor substrate 909, a strain generating portion about 20 to 100 xcexcm in thickness or a disk-shaped pressure receiving diaphragm 911 is formed. Besides, on the surface side of the diaphragm 911, four gauges 912 acting as a piezoresistance region is formed by the technique of impurity diffusion or ion implantation. And, a Wheatstone bridge is constituted of these and connected to the conductive pin 906 through a lead wire 913.
[Problem to be Solved by the Invention]
Because of being soft, however, the above solder materials 907 were apt to absorb a stress, but for some stationary chips, when the solder materials themselves solidify a stress was given to them to break the above sensor chips or to generate a drift in the measuring result of a sensor.
Besides, the above solder materials 907 were subject to oxidation, could not be preserved in air and therefore were inconvenient in handling.
[Means of Solution to the Problems]
Accordingly, it is the main object of the present invention to suppress the occurrence of a stress to a stationery chip and to enable the chip to be more easily fixed.
To attain such a object, a first invention in the present invention is so arranged that a die-bonding solder material comprises tin and gold and its substantial composition ratio is one which has the eutectic point with a more content of tin than that of gold.
As a result of such a composition, this die-bonding solder material increases in elongation percentage and tensile strength near room temperatures as compared with a solder material made of Snxe2x80x94Ag eutectic.
Besides, a second invention is so arranged as to add an additive made of a higher metal in eutectic point with gold alone than with both tin and gold, having a higher eutectic point than tin and forming no eutectic with tin, to the die-bonding solder material mentioned in the first invention in addition to tin and gold.
This additive is deposited as a simple substance first in the cooling process of a melting die-bonding solder material.
Besides, a third invention is the second invention with the added amount of an additive ranging from 0.1 to 9% by weight.
Besides, a fourth invention is the second invention with any of antimony, germanium or silicon employed as the additive.
Besides, a fifth invention is the first invention with the eutectic of tin and gold comprising substantially 95% to 90% of tin and 5% to 10% of gold.